Apparatus for wood chip digestion



Oct. 8, 1957 e. DURANT ETAL 2,809,111

APPARATUS FOR WOOD CHIP DIGESTION Filed Feb. 13, 1956 2 Sheets-Sheet 1Fl G.l.

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Filed Feb. 13, 1956 United States Patent APPARATUS FOR WOOD CHIPDIGESTION Leonard G. Durant, James E. Irvine, Rohe V. Pennington, andAiphonse Surino, Pittsfield, Mass., assignors to Candi EngineeringCorporation, Pittsfield, Mass., a corporation of MassachusettsApplication February 13, 1956, Serial No. 564,986

11 Claims. (Cl. 92--7) This invention relates to the continuousdigestion of cellulosic material such as wood-chips for making them intopulp. A current new type of such digestion treats the chips in a primaryenclosed tank or vessel wherein the chips in columnar formation arefirst steamed and then immersed in a pond of cooking liquor with whichthe chips are then impregnated. The chips are then evacuated from thevessel to a pipe wherein they are diluted with cooking liquor :to acontrollable pumpable consistency and are immediately pumped to adrainage station wherein they are drained of the liquor in which theyare immersed, whereupon they are pumped to a secondary vessel whereinthey are digested, again in columnar formation, but in non-submergenceand only in their absorbed and adsorbed liquor. When their digestion iscompleted, they are evacuated from :the digester and ejected from thesystem for subsequent treatment. This invention is directed to theconstruction and operation of such a drainage station. In such astation, the hot impregnated chips must be received while they are underpressure'and are in submergence in their cooking liquor. So it is anobject of this invention to provide ways and means for receiving them inthis condition and draining them of all but their absorbed and adsorbedliquor, meanwhile maintaining :them under the pressure and at thetemperature at which they are received. A further object is to devisemeans for aiding in the pumping of the chips from the evacuator in theimpregnating vessel to the drainage station by adding thereto sufiicientadditional cooking liquor to make the chips readily pumpable. Anotherobject is to entrap in the drainage station the tramp metal and otherheavy detritus which wood-chips usually have associated with them. Andanother object is to arrange for the ready removal of such entrappedcontaminants.

These and possibly other objects can be realized by interposing abovethe digester vessel in the system above described a drainage stationcomprising a main enclosing or housing inclined tank having a steam domerising from its lower end, a stack rising spacedly in the domesurrounded by an annular floor that closes oil the dome from the maintank, a fixed perforated drainer cylinder or second tank axiallydisposed within the main tank above its bottom, screw conveyor meansrotatable in the drainer for moving chips uphill therein to drain them,a chip-discharge outlet from the drainer, and a liquor-discharge outletfrom the tank below the drainer cylinder, with a feed of chips andliquor pumped tangentially into the space between the stack and thedome, means for regulating the dilution of submerged chips being pumpedtangentially into the dome, and means for removing from the annularfloor surrounding the stack tramp metal and detritus collecting thereonfrom the pumped feed of chips. In such an arrangement, the pumped chipsin appropriate liquor upon being tangentially fed to the steam domeswirl around the stack wherein they rise floatingly to spill over theupper edge or weir of the stack to descend therethrough into the drainercylinder, while tramp metal and detritus settles in the swirling mass tocollect on the ice annular floor around the stack, from which it isremoved from time to time. The moving chips drained during their passagealong the drainer cylinder, are discharged therefrom to the digester innon-submergence and have only their absorbed and adsorbed liquor.

The invention is illustrated in the accompanying drawings in whichFigure l is a somewhat diagrammatic side elevation, with parts insection, of a continuous digestion plant or system that forms theenvironment of the invention. Fig. 2 is a partial isometric view of adetail of the manifold used to inject either steam or liquor or bothinto the vessels. Fig. 3 is a vertical sectional view through thedrainage station. Fig. 4 is a horizontal sectional view taken along theline 44 in Fig. 3, indicating the tangential feed to the steam dome ofthe drainage station. Fig. 5 is an isometric view of the cylindricaldrainer 32.

Referring now to Figs. '1 and 2, showing the system, there is a chip-binA for receiving chips, or other cellulosic material to be treated,having an arch-breaker 11, and a suitable rotary chip-dischargingmechanism 12, operated by a variable speed motor driven mechanism 13,passes chips downwardly of the feed pipe 14 at a regulatable rate to amultivane chip feeding mechanism B for-delivering chips through pipe 15,valved as at 16 to and into a primary cylindrical tank or vessel Cdivided by a liquid-level L into an upper steaming zone D having a steamatmosphere 17 and a lower impregnating zone E made up of a pond ofcooking liquor 18. In the bottom of tank C (sometimes called theimpregnator vessel) there is an evacuator mechanism F for accomplishingcontinuous discharge of chips from the column thereof in the tank bymeans of a motor mechanism 19 driving a shaft 20, that rotatesblade-bearing arms 21 extending radially from a shroud 22 having anopening 23 therein through which chips are passed downwardly throughpipe 24 into pump 25 that forces the chips while submerged in cookingliquor and under pressure up through delivery conduit 26 to deliver themunder pressure tangentially to a drainage station G that comprises themain or outer steam-tight inclined :tank 27 having a steam dome 23 withan annular bottom 29 from which uprising a stack Sit) down which fallchips and liquor fed tangential to the steam dome 28 by the deliveryconduit 26. The chips and liquor swirl upwardly to spill over theupperweir-like edge of the stack 30, but meanwhile tramp metal or otherdetritus gravitates to the annular bottom or floor 29 from which it canbe removed through closable access means or other closable access meanssuch as hand-hole 31' and cover 31. Above the bottom of the maininclined tank 27, there is fixed an inner tank or cylindrical drainer 32having perforations 33, and rotatable therein is a screw conveyor 34.Thus chips and liquor descending through stack 30 enter drainer 32 upwhich the screw conveyor 34 moves them meanwhile their liquor drainsfrom them through the perforations 33-and flows from the tank throughoutlet 35 and pipe 36 for recovery treatment such as in accumulator tankJ. The chips that are so drained of the cooking liquor but whileretaining their absorbed and adsorbed liquor pass downwardly throughpipe 37, valved as at 33, into digestiontank or zone H, where the chipsare digested in non-submergence but in the presence of steam and theirown adsorbed and absorbed liquor. After being properly digested, theyare removed'from the digester tank or zone H by another evacuatormechanism F by means of a motor mechanism 19 driving a shaft 21), thatrotates blade-bearing arms 21 extending radially from a shroud 22 havingan opening 23' therein through which chips are passed downwardly throughpipe 24. But here pipe 24 leads into an axial flow ejector station I,from whence through pipes 39 and 40 digested chips are blown y a steamstream. to further treatment such as into a blow tank from which they goto refining or any other desired treatment. Since it usually becomesimportant to reclaim and otherwise controljthe cooking liquor used, Iindicates an-accumula-tor tank or station. Cooking liquor of controlledstrength ispumped by pump 47. from that tank I through suitableyalvedliquor inlet line 41'toa conventional automatic valve 42 controlled andregulated by a differential pressure type recording controller 43 forregulatingthe elevation of the liquid-level L of the pond 18 of cookingliquor so that it is maintained constant, or at least as nearly so aspossible. So the automatic valve 42 regulates the flow of liquor throughpipe 44 and its branches, eachof which leads to an annular manifold 45having injection nozzles such as 46 extending therefrom into the tank C,whereby liquor can be sprayed into the tank in a fairly well dispersedor distributed manner. The manifolds .45 are vdistributed along the tankC'as may seem desirable. Another-pipe 49 also leads from the accumulatortank I and goes to and into the pipe 24 for giving control of thequantity of liquor mixed with the chips discharged from tank C byevacuator F to make them pumpable (at a consistency of say by pump upthrough pipe 26'to the drainage station G. Still another pipe 48 is usedto lead from :the top of the accumulator tank I upwardly to the steamdome 23 of the drainage station G. Other valved pipes 47 and 57 leadinginto the accumulator tank I are for conducting certain incomingchemical-bearing liquids :thereinto.

From any suitable source, steam under pressure is supplied through steaminlet line 50 to the steaming zone D in the primary tank C by means ofan annular manifold 145 in all respects like manifold 45 and having thesame kind of injection nozzles 46 to supply steam into the tank, in awell distributed manner. The inlet of steam into the manifold 145 iscontrolled and regulated by a conventional pressure-temperaturerecording controller 51, that also controls and regulates valve 52 invapor-outflow line 53. And a final control is indicated generally at 55that is a chip level gauge and controller that consists of a transmittercontaining a radio-active material, and a receiver is connectedelectrically by connection W1 to the motor-drive 13 of chip bindischarger 12, to automatically regulate the chip level to besubstantially constant. The instrument is so mounted that the set pointcan be raised or lowered such as by pulley 56 by the operator. A similarchip-level sensing gauge and controller 55 is applied to the digesterzone or tank H, with its raising and loweringpulley 56 but in'this casethe controller 55 is connected by a connection W2 A to, and regulatesthe motor drive 19 on, the evacuator station F on the primary vessel C.

Digester zone or station H is provided with a steaminlet line 58, fordelivering steam under pressure to the branch lines 59 and 60, eachrespectively feeding steam to an annular manifold 245 having injectionnozzles, patterned after manifold 45'and its nozzles 46. Inlet of steamthrough line 58 is controlled and regulated by a conventionalpressure-temperature recording controller 61 (similar to controller 51)operating an automatic valve 62 and also an automatic'valve 63 includedin vapor outflow line 64. Valved vapor outlet pipe 65 from the steamdome 28 of the drainage station G, and also from valved vapor outletpipe 66 from the high point of the inclined tank 27 "of that station,can all join into a common exhaust line 67 leading to further treatmentof the vapors, if desired, suchas for turpentine recovery.

The continuous digestion of cellulosic material such as wood chipscarried out by this system in successive treatment zones may be said tocomprise feeding chips continuously to' the steaming zone where while incolumnar formation they are prepared for the ready aceptance of thecooking liquor by appropriate steaming, thus releasing non-condensablegases and otherwise preparingthe-chips for readyacceptance of thecooking liquor; next submerging the-thus conditioned chips-in hotcooking liquor under controlled conditions of time and temperature thatassure complete penetration and diffusion of the liquor into thechipsbut limit the chemical reaction therebetween so that in this zone ofimpregnating treatment, there is minimized any fiber-degrading action;the chips themselves now contain an amount of absorbed and adsorbedliquor of controlled chemical concentration suflicient to be cookedrapidly but insufficient to cause cellulose. degradation, so they aretransferred while in submergence and still under pressure from theimpregnation zone to a drainage zone where they are relieved of theirexcess liquor which drains freely therefrom during their uphillconveyance along the perforated cylindrical drainer therein; the drainedchips are then cooked also while in columnar formation in-only theirretained liquor and in non-submergence in a vaporous environmentenclosed in a digester; after being cooked, the chips are evacuated fromthe digester into an ejection zone having a receiver for the digestedchips,.from whence digested chips are ejected while in suspension insteam and projected or blown to a place of subsequent treatment. All ofthe action steps are carefully controlled as to pressure, temperature,andthe rate of downward movement or the time of transit of the chipsthrough each treatment zone andbetween such zones, which is a reason whythe chip level is maintained substantially constant in each of thevessels C and H; the.liquid-level L in vessel C is also so maintained;and the temperature and pressure of the steam is also carefullyautomatically controlled.

Referring again to the drainage station or zone G and to its details ofconstruction, the station has a main or outer tank or housing 27 that isinclined and is closed at its lower end by a dished cover 70 and at itsupper end by a dished cover 71, through which the screw conveyor 34 hasits shaft .72 pass to be supported by a journal 73 at its lower end andby a journal 74 at its upper end. The conveyor shaft is motivated by anysuitable motive power. In the main or outer tank 27 there is fixedlymounted eccentrically therein, a second or inner tank (see Fig. 5) witha drainer cylinder,32, having perforations 33 in its lower section andin its end. closures or walls 75 and 76. The drainer cylinder or innertank 32 is mounted concentrically around the conveyor 34 and its shaft72, which shaft is eccentrically mounted in main tank 27, so that thedrainer 32 has a space 77 between its bottom and the bottom of the maintank 27 that is substantially deeper than the space'78 between the topof the drainer 32 and the tankj27. A- space 79 is provided between theend wall 75 of the drainer and end cover 70 of the tank while another.such space 80 is provided between the end wall 76 of the drainer and endcover 71 of the tank so there is ample space all around the drainerwhereby it can be completely enveloped in a steam atmosphere. Thecylindrical drainer 32 has rising at a right angle from its lowersection, the stack 30 that is surrounded by the steam dome 28. The stackterminates at its open top in'a weir edge 81. Chips immersed in liquorare forcibly fed to the steam dome through pipe 26 that enters theperiphery of the steam dome through inlet opening 82 for delivering thechips tangentially into the steam dome and the space 83 between itsperipheral walls and the stack'30 inthe steam dome. The elevation of theinlet opening 82 corresponds to a line less than half the height ofeither the steam dome or the stack because it is desirable notonly'to'cause the incoming chips to swirl around the stack but to beforced upwardly or to surge upwardly to cause-all the chips in theirliquor to rise fioatingly and spill over the weir 81 down into andthrough thestack 30. In spite of this upward surge, tramp metal and.other heavier detritus settles therethrough to collect on the annularbottom or floor 29 from which it can be removed from time to timethrough the ports or-hand-holes 31'. The tank 27 is inclined downwardlytoward its steam domed end at an angle of about 7, substantially as thatshown. this-isio assure drainagefrom the chips of all but their Thereason forabsorbed and adsorbed liquor as they are moved up-hill overthe draining perforations, that is, conveyed up the incline of thecylindrical drainer 32 whereupon they fall vertically through the chipdischarge outlet pipe 37, that passes from the drainer to a placeoutside of the tank 27.

So in operation, the impregnated chips discharged with their liquor bythe evacuator station F from impregnation zone E, are pumped by pump 25,with liquor added through pipe 49 to make the chips thoroughly pumpable,up through delivery conduit 26, to the drainage station or Zone G.Through tangential inlet opening 82 into the steam dome 23, the chipsand their liquor are swirled around the stack 30 as shown by the arrowsin Fig. 3, to floatingly surge upwardly until they reach the elevationof weir edge 81 of the stack over which the chips and their liquor spilland descend down the stack into the cylindrical drainer or inner tank27. The chips are moved upwardly along the inclined drainer by the screwconveyor 34, meanwhile being drained of their liquor that drains awayfrom the moving chips through the perforations 33 to be received by thespace 77 beneath the bottom of the inner tank or drainer, from whencethe liquor flows away and downwardly through liquor discharge pipe 36 tosubsequent treatment or recovery. The drained chips moved uphill by thescrew conveyor 34 fall down vertical chip discharge pipe 37 that leadsthem, with only their absorbed and absorbed liquor, into the digestertank H.

The temperature and pressure surrounding the chips is maintained bysteam from two sources. The drainer is open to the digester through thelarge pipe 37 and valve 38 so that digester pressure and temperature aremaintained. The dome 28 is also connected through equalizing pipe 48 tothe accumulator J whence steam can be introduced to the dome 28. Thechips flow down through the stack 30 to fill the inner tank 32 fromwhich liquor drains through the perforations 33 to fill the spacesurrounding the inner tank 32 and from which space vapors andnon-condensible gases can be drawn off through valved outlet pipes 65and 66, that can be seen from Fig. l, to join pipe 67 carrying suchvapors to subsequent treatment such as turpentine recovery. Theperforations in the low end wall 75 will be helpful in draining liquorfrom the chips while the perforations in the upper end wall 76 willallow steam pressure from the digester coming up through pipe 37 to passeasily into the spaces 77, 78, 79 and 80. Since the pressure in thedrainage station G is the same as the pressure in the impregnator tankE, there is the same pressure on each side of pump 25, and thisfacilitates very much the operation of that device. The drainer thendrains chips of all but their absorbed and adsorbed liquor while in ahigh pressure high temperature steam atmosphere. The drainer stationsteam pressure normally used will be that of the digester H that rangesordinarily from 100 to 170 pounds per square inch gauge pressure.

As this invention may be embodied in several forms without departingfrom the spirit or essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims and all changesthat fall Within the metes and bounds of the claims or that form theirfunctional as well as conjointly cooperative equivalents, are thereforeintended to be embraced by those claims.

We claim:

1. Continuously operable wood-chip digesting apparatus which comprises asystem having a combined steaming and impregnating tank enclosed forholding a pond of cooking liquor overlain by a steam atmosphere, meansfor regulatably supplying steam to the tank, means for regulatablyfeeding chips to the steam atmosphere, means for feeding such liquor tothe pond, means for maintaining a constant liquid-level on the pond, achip drainage station, pump means and a pipe for regulating delivery tothe drainage station of impregnated chips immersed in liquor, a chipdigester under pressure enclosing a steam atmos phere, means for passingchips from the drainage station to the digester, means for supplyingsteam to the digester for controlling its temperature, and means fordischarging digested chips from the digester; wherein the drainagestation comprises a steam-tight inclined enclosing cylindrical tankhaving a steam dome rising from its lower end, a perforated cylindricaldrainer longitudinally disposed in the tank above the bottom of thetank, a stack rising spacedly in the dome from the drainer surrounded byan annular floor that closes off the dome from the tank, said deliverypipe delivering chips tangentially into the space between the stack andthe steam dome, screw conveyormeans rotatable in the drainer, achip-discharge outlet from the drainer, and a liquor-discharge outletfrom the tank below the drainer.

2. Apparatus according to claim 1, with the addition of means for addingcooking liquor to the pump means for regulatably diluting theconsistency of the submerged chips being pumped to the drainer.

3. Apparatus according to claim 1, with the addition of closable accessmeans through which can be removed tramp metal and detritus settling toand collecting on the annular fioor surrounding the stack in the steamdome.

4. Apparatus according to claim 1, with means for maintainingsubstantially the same steam pressure on each side of the pump meansdelivering submerged chips to the drainer.

5. Apparatus according to claim 1, wherein the cylindrical drainer iseccentrically mounted in the tank.

6. Apparatus according to claim 1, wherein the drainer is perforated inits lower longitudinal section with a closed upper longitudinal sectionwhile the stack rises through the tank into the steam dome from theperiphery of the closed upper section of the drainer.

7. A chip-digesting system, comprising means for digesting chips whilein submergence; means for feeding chips thereto; means for drainingchips received from the digester that includes a main enclosing inclinedsteamtight cylindrical tank having at its lower end a bottomdrained-liquor discharge outlet and a chip-receiving steam dome risingfrom its upper end, a cylindrical drainer eccentrically disposed in thetank having a perforated bottom section through which liquor from thechips drains from the drainer into the tank, an open-ended stack intowhich chips cascade from the dome rising from the top of the lower endof the drainer to and into the steam dome while providing an annularspace between it and the dome, an annular floor surrounding the stackclosing off the bottom of that space, a motivated screw conveyor mountedlongitudinally and concentrically in the drainer while eccentricallyjournalled in the ends of the tank for moving chips from the stack alongthe drainer, and a chip discharge outlet receiving chips from theconveyor leading from the bottom of the higher end of the drainer andextending through the tank bottom to the outside thereof, and chipdelivery means for forcibly feeding a supply of chips immersed incooking liquor tangentially into the space between the stack and thedome at an elevation from which they swirlingly and fioatingly surgeupwardly to spill over the open top of the stack.

8. Apparatus according to claim 7, with means includinga port and covertherefor in the steam dome adjacent the annular floor therein forremoval therethrough of tramp metal and detritus descending from theupwardly swirling chips and collecting thereof.

9. A chip-digesting system, comprising means for digesting chips whilein submergence; means for feeding chips thereto; means for drainingchips received from the digester that includes an outer main enclosinginclined steam-tight cylindrical tank having at its lower end a bottomdrained-liquor discharge outlet and a chip-receiving steam dome risingfrom its upper end, an inner second cylindrical drainer tank locatedwithin the main tank having aperforated; bottom... section through whichliquor frornchips 'within the secondtank drainsfrorn the latter into'themain tank, an:,open-ended stack into which chips cascade from the domerising from the top of the lower end of the second tankto and into thesteam dome while providing, an, annular space between it and the dome, amotivated screw conveyor mounted longitudinally andconcentrically'within the second tank for moving chips from the stackalong the drainer, a shaft for the screw conveyor passing through themain tank and journalled therefrom, a chip discharge outlet pipereceiving chips from the conveyor and leading from the bottom of thehigher end of the second tank and extending therefrom through the maintank, and means for supplying steam to the steam dome, and means forforcibly feeding a supply of chips and-liquor tangentially into thespace between the stack and the dome for swirling the chips and liquorupwardly to spill over into the stack and fall into the second. tank,whichstack forms the only pathway whereby chips .reachthe inner tank andthe perforations in the inner tank form the only pathway whereby liquorfrom the chips reaches the outer tank.

10. Apparatus according to claim 9, wherein the stack References Citedin the file of this patent UNITED STATES PATENTS 1,915,812 WollenbergJune 27, 1933 1,932,885 Dunbar Oct. 31, 1933 2,159,258 De La Roza May23, 1939 2,542,801 De La-Roza Feb. 20, 1951 2,614,923 Tark Konen Oct.21, 1952 2,673,690 Segl Mar. 30, 1954 FOREIGN PATENTS 111,424 AustraliaAug. 28, 1940

7. A CHIP-DIGESTING SYSTEM, COMPRISING MEANS FOR DIGESTING CHIPS WHILESUBMERGENCE; MEANS FOR FEEDING CHIPS THERETO; MEANS FOR DRAINING CHIPSRECEIVED FROM THE DIGESTER THAT INCLUDES A MAIN ENCLOSING INCLINEDSTEAMTIGHT CYLINDRICAL TANK HAVING AT ITS LOWER END A BOTTOMDRAINED-LIQUOR DISCHARGE OUTLET AND A CHIP-RECEIVING STEAM DOME RISINGFROM ITS UPPER END, A CYLINDRICAL DRAINER ECCENTRICALLY DISPOSED IN THETANK HAVING A PERFORATED BOTTOM SECTION THROUGH WHICH LIQUOR FROM THECHIPS DRAINS FROM THE DRAINER INTO THE TANK, AN OPEN-ENDED STACK INTOWHICH CHIPS CASCADE FROM THE DOME RISING FROM THE STEAM OF THE LOWER ENDOF THE DRAINER TO AND INTO THE STEAM DOME WHILE PROVIDING AN ANNULARSPACE BETWEEN IT AND THE DOME, AN ANNULAR FLOOR SURROUNDING THE STACKCLOSING OFF THE BOTTOM OF THAT SPACE, A MOTIVATED SCREW CONVEYOR MOUNTEDLONGITUDINALLY AND CONCENTRICALLY IN THE DRAINER WHILE ECCENTRICALLYJOURNALLED IN THE ENDS OF THE TANK FOR MOVING CHIPS FROM THE STACK ALONGTHE DRAINER, AND A CHIP DISCHARGE OUTLET RECEIVING CHIPS FROM THECONVEYORR LEADING FROM THE BOTTOM OF THE HIGHER END OF THE DRAINER ANDEXTENDING THROUGH THE TANK BOTTOM TO THE OUTSIDE THEREOF, AND CHIPDELIVERY MEANS FOR FORCIBLY FEEDING A SUPPLY OF CHIPS IMMERSED INCOOKING LIQUOR TANGENTIALLY INTO THE SPACE BETWEEN THE STACK AND THEDOME AT AN ELEVATION FROM WHICH THEY SWIRLINGLY AND FLOATINGLY SURGEUPWARDLY TO SPILL OVER THE OPEN TOP OF THE STACK.